This invention relates to a pneumatically powered installation tool for installing fasteners such as lockbolts, i.e. fasteners comprising a groove stem including a breaker groove, and a collar.
Known tools for installing lockbolt fasteners install the lockbolt into a workpiece by swaging the collar onto the grooved stem. On depression of the tool trigger, a pull stroke is initiated, whereby compressed air is fed to one side of a double-acting pneumatic piston, thereby causing movement of the piston and of an intensifier rod which is coupled to the piston. The movement of the piston and rod causes movement of a head piston, which in turn causes actuation of the jaws within the tool head. The tool applies a pulling force to the stem of a fastener via the jaws, thereby causing a collar to be swaged onto the stem. The pulling force is applied until the stem is caused to break at the breaker groove. The tool applies a ‘push-off’ force via reversed movement of the head piston, to eject the collar from the tool head.
After the trigger is released, a return stroke is initiated whereby the head piston and the pneumatic piston return to their original positions.
In currently known lockbolt installation tools, two hydraulic lines are provided to the head to produce the double-acting piston motion which is required to install the lockbolt. These hydraulic lines are usually provided by the double-acting pneumatic piston which actuates the intensifier rod which acts in both directions of movement.
However, in prior art tools in which the two hydraulic lines are of fixed volumes, any oil loss in the pull side causes a loss of stroke and a vacuum condition during the return stroke, causing aeration of the oil and reduced tool performance. Any oil loss in the return side prevents the head piston from fully returning, which in turn results in reduced engagement of the tool jaws on the lockbolt stem, thereby increasing the chance of failure of the tool nose equipment or the lockbolt.
To counter the above effect, an oil reservoir and a pressure relief valve is normally used to provide a secondary circuit, providing additional hydraulic volume. Oil from the reservoir is drawn in when there is an imbalance in the oil volumes, and when the head returns to its end stop, any excess volume is pushed through the pressure relief valve.
The provision of the oil reservoir and pressure relief valve increases tool complexity, bulk, and cost. Furthermore, if the pressure relief output valve is connected to the pull side, and there is an obstruction preventing the head from fully returning, excess oil is discharged into the pull side. This results in the head piston starting the cycle partially back, thereby again reducing engagement of the tool jaws with the grooved stem of the lockbolt, and increasing the chance of failure of the tool nose equipment or the lockbolt.
An aim of the current invention is to provide a lockbolt installation tool which does not suffer from a gradual loss of stroke, which ensures full engagement of the tool jaws with the grooved lockbolt stem and thereby prevents potential failure of the tool nose equipment or the lockbolt.
Accordingly the present invention comprises a pneumatically powered fastener installation tool comprising a head section, a handle section, and pneumatic installation means comprising a pneumatic piston coupled to an intensifier rod, wherein the intensifier rod extends into a main channel within the handle section of the tool, and wherein a pull piston and a return piston are provided within the main channel, and wherein the pull piston and the return piston are free to move within the main channel in a direction axially with respect to the main channel and wherein in use, the tool conducts a cycle comprising a pull stroke and a return stroke thereby to install a fastener.
The present invention uses floating pistons to provide compliance when transmitting pressure from the double acting pneumatic piston to the head piston. In the volume between the floating pistons, air is provided via a vent to atmosphere. The floating pistons are free to take whatever position dependent upon the hydraulic displacement. Any oil loss on the pull stroke will not cause a vacuum condition in the oil volumes within the tool.
A first embodiment of the present invention includes a secondary oil circuit, comprising a positively pressured oil reservoir connected via a check valve and a pressure relief valve (in parallel) to the return side of the main channel.
In a second embodiment aspect of the present invention, a secondary reservoir is not provided. Instead, an integrated reservoir is provided by an excess of oil in the return volume itself. Therefore, there is a lost pneumatic piston stroke in a normal cycle. However, if oil is lost from the return side, extra pneumatic piston stroke is available. As oil is lost, the hydraulic pull and return pistons move apart from each other within the main channel.
Preferably a seal is provided, which is fitted to the pneumatic piston, and acts to seal the air inlet/exhaust on the pull side when the pneumatic piston is at the end of the return stroke.
Preferably a small diameter aperture through the pneumatic piston is also provided. The aperture acts as an air bleed across the piston, i.e. between the pull and return sides of the pneumatic piston, thereby equalising the pressures on either side when the tool is at rest. As there is a larger area on the return side of the pneumatic piston, pressure is always maintained on the seal to ensure sealing. However, the pressure on the return side of the head piston is greatly reduced.
The seal and the small diameter aperture act to reduce the hydraulic pressure which is held on the return side of the head piston during tool inactivity.
Because the reservoir in the second embodiment is integrated, the component count of the tool is reduced, and tool complexity, bulk and cost are reduced.